These components correspond to testing the sense of smell (I), visual fields and acuity (II), eye movements (III, IV, VI) and pupils (III, sympathetic and parasympathetic), sensory function of face (V), strength of facial (VII) and shoulder girdle muscles (XI), hearing and balance (VII, VIII), taste (VII, IX, X), pharyngeal movement and reflex (IX, X), tongue movements (XII).

The neurons in the olfactory epithelium have a limited life span, and new cells grow to replace the ones that die off.

The axons from these neurons grow back into the CNS by following the existing axons—representing one of the few examples of such growth in the mature nervous system.

If all of the fibers are sheared when the brain moves within the cranium, such as in a motor vehicle accident, then no axons can find their way back to the olfactory bulb to re-establish connections.

As the name suggests, the abducens nerve is responsible for abducting the eye, which it controls through contraction of the lateral rectus muscle.

Testing this is as simple as introducing salty, sour, bitter, or sweet stimuli to either side of the tongue.

Stimuli applied to specific locations on the tongue will dissolve into the saliva and may stimulate taste buds connected to either the left or right of the nerves, masking any lateral deficits.

A vibrating tuning fork is placed on the mastoid process and the patient indicates when the sound produced from this is no longer present.

With unilateral sensorineural hearing loss, however, damage to the cochlea or associated nervous tissue means that the tuning fork sounds quieter in that ear.